1. Field of Invention
The present invention relates to a projection display device, and more particularly, to a technique for achieving size reduction and for efficiently cooling an optical system including optical modulation devices inside the device.
2. Description of Related Art
Hitherto, a projection display device has been known which comprises a light-source lamp, an optical system for forming an optical image according to image information by optically processing a light beam emitted from the light-source lamp, a projection lens for enlarging and projecting the image formed by the optical system onto a projection plane, and a power supply for supplying electric power for driving the device. In such a projection display device, the optical system generally includes a color separation optical system for separating light from the light-source lamp into three colors, optical modulation devices for respectively modulating the separated three color beams, and a color synthesizing prism for synthesizing the modulated light beams. The optical modulation devices are placed on a head body having high rigidity inside the device so that images formed by the three optical modulation devices will not be projected offset from one another.
Such projection display devices are widely used for multimedia presentations at conferences, academic meetings, exhibitions, and the like.
While the projection display device is sometimes kept installed in a conference room or the like for a presentation, it is sometimes brought in as necessary, or is stored in another place after use. Therefore, improved portability of the projection display device is desirable to facilitate transportation, and the device must be further reduced in size.
In reducing the size of the device, however, various components are densely placed inside the device, and it is difficult to circulate cooling air drawn in by a fan or the like. Therefore, devices are adopted to sufficiently cool heat-producing components. Since the optical modulation devices are particularly apt to produce heat, a cooling air inlet is provided below the optical modulation devices so as to cool the optical modulation devices, and forcible cooling is performed by an intake fan disposed on the lower surface of the head body. A general type of intake fan is mounted to a rectangular frame, and is fixed by screwing four corners of the frame to the lower surface of the head body.
A structure in which the fan is always fixed at four corners, however, sometimes hinders reduction in size and thickness of the device. For example, (1) when the front side (projection lens side) of the head body is thickened to secure a margin for mounting the fan, the head body becomes large, which is contrary to the purpose of reducing the size of the overall device. (2) When the fan is mounted on the head body offset to the rear side in order to solve this problem, since the rotation center of the fan and the midpoint among the three optical modulation devices are misaligned, it is difficult to uniformly cool the optical modulation devices. (3) When a small intake fan is employed to align the center of the intake fan with the midpoint among the three optical modulation devices, cooling is insufficient.